Cooperative Breeding Behavior Research Articles

Ecogeography of group size suggests differences in drivers of sociality among cooperatively breeding fairywrens.

Cooperatively breeding species exhibit a range of social behaviours associated with different costs and benefits to group living, often in association with different environmental conditions. For example, recent phylogenetic studies have collectively shown that the evolution and distribution of cooperative breeding behaviour is related to the environment. However, little is known about how environmental variation may drive differences in social systems across populations within species, and how the relationship between environmental conditions and sociality may differ across species. Here, we examine variation in social group size along a steep environmental gradient for two congeneric cooperatively breeding species of fairywrens (Maluridae) and show that they exhibit opposing ecogeographic patterns. Purple-backed fairywrens, a species in which helpers increase group productivity, have larger groups in hot, dry environments and smaller groups in cool, wet environments. By contrast, superb fairywrens, a species with helpers that do not increase group productivity despite the presence of alloparental care, exhibit the opposite trend. We suggest differences in the costs and benefits of sociality contribute to these opposing ecogeographical patterns and demonstrate that comparisons of intraspecific patterns of social variation across species can provide insight into how ecology shapes social systems.

Genome survey sequencing and mining of genome-wide microsatellite markers in yellow-billed babbler (Turdoides affinis)

Turdoides affinis is a species of group dwelling old world passerine of family Leiothrichidae. Unavailability of genome-wide sequence and species-specific molecular markers have hindered comprehensive understanding of cooperative breeding behaviour in T. affinis. Therefore, we generated genome-wide microsatellite markers through whole genome short read sequencing of T. affinis. A total of 68.8 gigabytes of paired-end raw data were sequenced containing 195,067,054 reads. Total sequenced reads spanned a coverage of 17X with genome size of 1.18 Gb. A large number of microsatellite markers (265,297) were mined in the T. affinis genome using Krait, and 50 most informative markers were identified and validated further. In-silico PCR results validated 47 markers. Of these 47 markers, five were randomly selected and validated in-vitro in twelve individuals of T. affinis. Genotyping data on these five loci estimated observed heterozygosity (H0) and expected heterozygosity (He) ratios between 0.333 – 0.833 and 0.851–0.906, respectively. Effective allele size ranged from 6.698 to 10.667, inbreeding coefficient of the population ranged from 0.080 to 0.631 and null allele frequency was calculated at 0.055 to 0.303. Polymorphic information content of all the five loci varied between 0.850 and 0.906. Probabilities of exclusion and identity across 5 loci was estimated to be 0.95 and 0.0036, respectively. All the loci showed significant adherence to Hardy-Weinberg equilibrium. The microsatellite markers reported in this study will facilitate future population genetics studies on T. affinis and other congeneric species.

Genomic signatures and evolutionary history of the endangered blue-crowned laughingthrush and other Garrulax species

BackgroundThe blue-crowned laughingthrush (Garrulax courtoisi) is a critically endangered songbird endemic to Wuyuan, China, with population of ~323 individuals. It has attracted widespread attention, but the lack of a published genome has limited research and species protection.ResultsWe report two laughingthrush genome assemblies and reveal the taxonomic status of laughingthrush species among 25 common avian species according to the comparative genomic analysis. The blue-crowned laughingthrush, black-throated laughingthrush, masked laughingthrush, white-browed laughingthrush, and rusty laughingthrush showed a close genetic relationship, and they diverged from a common ancestor between ~2.81 and 12.31 million years ago estimated by the population structure and divergence analysis using 66 whole-genome sequencing birds from eight laughingthrush species and one out group (Cyanopica cyanus). Population inference revealed that the laughingthrush species experienced a rapid population decline during the last ice age and a serious bottleneck caused by a cold wave during the Chinese Song Dynasty (960–1279 AD). The blue-crowned laughingthrush is still in a bottleneck, which may be the result of a cold wave together with human exploitation. Interestingly, the existing blue-crowned laughingthrush exhibits extremely rich genetic diversity compared to other laughingthrushes. These genetic characteristics and demographic inference patterns suggest a genetic heritage of population abundance in the blue-crowned laughingthrush. The results also suggest that fewer deleterious mutations in the blue-crowned laughingthrush genomes have allowed them to thrive even with a small population size. We believe that cooperative breeding behavior and a long reproduction period may enable the blue-crowned laughingthrush to maintain genetic diversity and avoid inbreeding depression. We identified 43 short tandem repeats that can be used as markers to identify the sex of the blue-crowned laughingthrush and aid in its genetic conservation.ConclusionsThis study supplies the missing reference genome of laughingthrush, provides insight into the genetic variability, evolutionary potential, and molecular ecology of laughingthrush and provides a genomic resource for future research and conservation.

Cooperative breeding behavior emerges early in restored populations of the Brown-headed Nuthatch (Sitta pusilla)

We monitored the emergence of cooperative breeding behavior in 2 Brown-headed Nuthatch (Sitta pusilla) populations that were reintroduced to formerly occupied sites in south Florida. Individuals from presumed family groups were captured and moved (n = 48) in the first reintroduction attempt (1998–2001) on Everglades National Park, Florida, USA. Two cooperative breeding groups were observed in the second breeding season (2000) and the proportion of cooperative breeding groups increased to ∼20% of the territories present in year 5. The second reintroduction attempt focused on capture and release of juveniles (n = 30) onto Jonathan Dickinson State Park, Florida, USA. A cooperative breeding group was observed in the first breeding season (2019) of this second attempt and in the 2 breeding seasons that followed (2020–2021). Cooperative breeding behavior was observed in both reintroduction attempts when nuthatches occupied a small fraction of the available habitat. Habitat saturation has been linked to cooperative breeding behavior in other avian taxa, but our observations point to the potential influence of other factors in promoting cooperation in the nuthatch. Recent studies suggest these factors might include mate limitations, benefits derived from group activities, and direct benefits of co-breeding among >2 adults.

Manipulated sex ratios alter group structure and cooperation in the brown-headed nuthatch

Abstract A biased adult sex ratio (ASR) can influence cooperative breeding behavior if the bias limits mating opportunities for the more abundant sex. We tested predictions associated with the ASR-cooperation hypothesis in the brown-headed nuthatch (Sitta pusilla). We manipulated ASR by cross-fostering known-sex nestlings within 2 large (≥100 ha) experimental plots for 5 years using a crossover design where each plot received an opposing male- or female-biased treatment for 2 consecutive years. A year with no manipulations followed before the bias was reversed on each plot for 2 additional years. Variation in ASR (adult males/total adults) was pronounced compared to background proportions (0.55) and ranged from a female bias in female-biased plots (0.47) to a strong male bias in male-biased plots (0.71). Sex ratios during the postbreeding period ranged more broadly (0.33 in female-biased plots vs. 0.74 in male-biased plots). Territory densities did not change significantly and allowed 6 predictions to be assessed. Consistent with predictions, the prevalence of cooperative breeding groups doubled under male-biased treatments and large cooperative groups appeared (≥2 male helpers vs. the single male helper most common prior to the experiment). These changes occurred despite increased dispersal of cross-fostered males in male-biased plots. Most juvenile females dispersed, but, consistent with predictions, the prevalence of female helpers increased under female-biased treatments. Manipulations did not alter the sex of nestlings produced nor extend the time that males served as helpers. Taken collectively, results support the ASR-cooperation hypothesis and the role that mate limitations play in cooperative breeding behavior.

Experimentally evoked same-sex sexual behaviour in pigeons: better to be in a female-female pair than alone

Same-sex sexual behaviour has been noted among social animals. However, because of the large number of observations necessary, data from controlled experiments are lacking. In this study, we performed experiments to evaluate the effects of male and female removal in colonies of the feral pigeon (Columba livia f. urbana). After the experimental removal of males, five long-lasting female-female pairs occurred. We found that those pairs could successfully raise offspring in a manner comparable to female-male pairs. Same-sex sexual behaviour and pairing in females is thus a better alternative to postponed breeding or breeding alone without the help of a partner. In contrast, in the case of female-removal experiments, same-sex pairing behaviour occurred in males as a temporary phenomenon with characteristic mutual aggression. Additionally, under a male-biased sex ratio, we observed father-son and father-daughter copulations. To the best of our knowledge, these results are the first obtained under controlled experimental conditions which demonstrate that the sex ratio of a population can shift the social structure and cause cooperative same-sex breeding behaviour to arise in a monogamous species.

The ecology of cooperative breeding behaviour.

Ecology is a fundamental driving force for the evolutionary transition from solitary living to breeding cooperatively in groups. However, the fact that both benign and harsh, as well as stable and fluctuating, environments can favour the evolution of cooperative breeding behaviour constitutes a paradox of environmental quality and sociality. Here, we propose a new model - the dual benefits framework - for resolving this paradox. Our framework distinguishes between two categories of grouping benefits - resource defence benefits that derive from group-defended critical resources and collective action benefits that result from social cooperation among group members - and uses insider-outsider conflict theory to simultaneously consider the interests of current group members (insiders) and potential joiners (outsiders) in determining optimal group size. We argue that the different grouping benefits realised from resource defence and collective action profoundly affect insider-outsider conflict resolution, resulting in predictable differences in the per capita productivity, stable group size, kin structure and stability of the social group. We also suggest that different types of environmental variation (spatial vs. temporal) select for societies that form because of the different grouping benefits, thus helping to resolve the paradox of why cooperative breeding evolves in such different types of environments.

Nesting Ecology of Tibetan Sand MartinsRiparia riparia,with Special Reference to Cooperative Breeding

Abstract The Sand Martin Riparia riparia is a widely distributed species, but its natural history at high elevation is poorly understood. In this paper, we describe their nesting ecology and their cooperative breeding behavior at an altitude of 3,400 m on the northeast Tibetan plateau. After arriving on their breeding grounds in early May, pairs nested solitarily, excavating nests burrows themselves into vertical stream banks. Burrows averaged 113 cm long. The clutch, averaging 4.9 pure white eggs, was laid during late May and June. Incubation, shared by both parents, lasted 14.7 days, and the young fledged at an average of 23.3 days of age. They were single-brooded and had an overall nest success of 89.5%. Cooperative breeding was observed in two out of 19 nests; in each case a single male attendant assisted the parents. This special social system has not previously been described in this species. More feeding visits were made to the cooperative nests than to non-cooperative nests and the brood size at f...

Adult helpers increase the recruitment of closely related offspring in the cooperatively breeding rifleman.

Indirect fitness benefits gained through kin-selected helping are widely invoked to explain the evolution of cooperative breeding behavior in birds. However, the impact of helpers on productivity of helped broods can be difficult to determine if the effects are confounded by territory quality or if the benefit of helpers is apparent only in the long term. In riflemen Acanthisitta chloris, helping and group membership are effectively decoupled as adult helpers are individuals that have dispersed from their natal territory and live independently from breeders in "kin neighborhoods." Nevertheless, helpers direct their care toward close relatives, suggesting that helping provides indirect fitness benefits. The aim of this study was to examine the benefits of helpers to recipient offspring in the rifleman, investigating both short- and long-term effects. The total amount of food delivered to nestlings in helped broods was greater than that received by broods without helpers. This did not result in any short-term increase in nestling mass or nestling body condition nor was there any reduction in length of the nestling period at helped nests. However, helpers were associated with a significant increase in juvenile recruitment, with twice the proportion of fledglings surviving to the next breeding season from helped broods relative to unhelped broods. Thus, helpers gain indirect fitness by improving the survival of kin, and in contrast to a previous study of riflemen, we conclude that kin selection has played a key role in the evolution of cooperative breeding in this species.

Post‐fragmentation population structure in a cooperative breeding Afrotropical cloud forest bird: emergence of a source‐sink population network

The impact of demographic parameters on the genetic population structure and viability of organisms is a long-standing issue in the study of fragmented populations. Demographic and genetic tools are now readily available to estimate census and effective population sizes and migration and gene flow rates with increasing precision. Here we analysed the demography and genetic population structure over a recent 15-year time span in five remnant populations of Cabanis's greenbul (Phyllastrephus cabanisi), a cooperative breeding bird in a severely fragmented cloud forest habitat. Contrary to our expectation, genetic admixture and effective population sizes slightly increased, rather than decreased between our two sampling periods. In spite of small effective population sizes in tiny forest remnants, none of the populations showed evidence of a recent population bottleneck. Approximate Bayesian modelling, however, suggested that differentiation of the populations coincided at least partially with an episode of habitat fragmentation. The ratio of meta-Ne to meta-Nc was relatively low for birds, which is expected for cooperative breeding species, while Ne /Nc ratios strongly varied among local populations. While the overall trend of increasing population sizes and genetic admixture may suggest that Cabanis's greenbuls increasingly cope with fragmentation, the time period over which these trends were documented is rather short relative to the average longevity of tropical species. Furthermore, the critically low Nc in the small forest remnants keep the species prone to demographic and environmental stochasticity, and it remains open if, and to what extent, its cooperative breeding behaviour helps to buffer such effects.

Dominance, not kinship, determines individual position within the communal roosts of a cooperatively breeding bird

Kin selection has played an important role in the evolution and maintenance of cooperative breeding behaviour in many bird species. However, although relatedness has been shown to affect the investment decisions of helpers in such systems, less is known about the role that kin discrimination plays in other contexts, such as communal roosting. Individuals that roost communally benefit from reduced overnight heat loss, but the exact benefit derived depends on an individual's position in the roost which in turn is likely to be influenced by its position in its flock's dominance hierarchy. We studied the effects of kinship and other factors (sex, age, body size and flock sex ratio) on an individual's roosting position and dominance status in captive flocks of cooperatively breeding long-tailed tits Aegithalos caudatus. We found that overall, kinship had little influence on either variable tested; kinship had no effect on a bird's position in its flock's dominance hierarchy and the effect of kinship on roosting position was dependent on the bird's size. Males were generally dominant over females and birds were more likely to occupy preferred roosting positions if they were male, old and of high status. In this context, the effect of kinship on social interactions appears to be less important than the effects of other factors, possibly due to the complex kin structure of winter flocks compared to breeding groups.

Spatiotemporal environmental variation, risk aversion, and the evolution of cooperative breeding as a bet-hedging strategy

In cooperatively breeding systems in which some individuals delay reproduction to help raise others' offspring, environmental variation in space and time influences individual reproductive strategies as well as interspecific patterns of sociality. Although most environmental explanations for cooperative breeding emphasize the mean fitness gains of living socially, the fittest individuals are not always those that produce on average the highest number of offspring. At times, variance in fecundity can influence fitness as much as mean fecundity, particularly in small populations like those of cooperative breeders. Cooperative breeding behavior could therefore be a risk-averse strategy to maximize fitness by reducing environmentally induced fecundity variance. Such a within-generation bet-hedging hypothesis for social evolution predicts that (i) variance in reproductive success should be related to environmental variation, (ii) variance in reproductive success should be related to the potential for cooperation in a group, and (iii) the potential for cooperation should be related to environmental variation. Using data from a 10-y study of cooperatively breeding superb starlings (Lamprotornis superbus) living in a temporally and spatially variable savanna ecosystem, I found that variance in reproductive success declined with increasing environmental quality (temporal variation), increasing territory quality (spatial variation), and increasing group size (potential for cooperation), which is itself related to environmental variation. To understand the adaptive value of cooperative breeding behavior in variable environments, researchers must consider both mean and environmentally induced variance in fecundity. Determining how spatiotemporal environmental variation drives risk-averse strategies may provide insights into the evolution of complex social behavior.

Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds

Understanding why organisms as different as amoebas, ants, and birds cooperate remains an important question in evolutionary biology. Although ecology can influence cooperation and conflict within animal societies and has been implicated in species differences in sociality, the environmental predictors of sociality across broad geographic and taxonomic scales remain poorly understood. In particular, the importance of temporal variation in selection pressure has been underestimated in most evolutionary studies. Environmental uncertainty resulting from climatic variation is likely to be an important driver of temporal variation in selection pressure and therefore is expected to impact the evolution of behavioral, morphological, and physiological traits, including cooperation. Using a data set of over 95% of the world's birds, we examine the global geography and environmental, biotic, and historical biogeographic predictors of avian social behavior. We find dramatic spatial variation in social behavior for which environmental and biotic factors--namely, among-year environmental variability in precipitation--are important predictors. Although the clear global biogeographic structure in avian social behavior carries a strong signal of evolutionary history, environmental uncertainty plays an additional key role in explaining the incidence and distribution of avian cooperative breeding behavior.

Nesting and Cooperative Breeding Behaviours of a High-Altitude Babbler, Tibetan BabaxBabax koslowi

The Tibetan Babax is a high-altitude babbler endemic to the NE Tibetan plateau. This is the first report of the species nesting behaviour: the study was based on information gathered during 2005 and 2006 in the upper Mekong River basin (32°N, 96°E, 3700–4300 m.a.s.l.), S Qinghai. The birds nested low (< 2 m) in conifers and laid eggs from early May to late July. The clutch size was 3–4 eggs. Nestlings fledged at 13–14 days, when they reached 52% of the adult female weight. In all four nesting attempts (three nests and one post-fledging social unit), more than two birds (3-6) were observed feeding the young or guarding the nest against conspecific intruders or potential predators. These results indicate that all three member species of the genus Babax (the two others are the high-altitude Giant Babax and the lowland Chinese Babax) display a cooperative breeding system. This provides a good example of phylogeny as a component responsible for the evolution of cooperative breeding behaviour.

Temporal Environmental Variability Drives the Evolution of Cooperative Breeding in Birds

Many vertebrates breed in cooperative groups in which more than two members provide care for young. Studies of cooperative breeding behavior within species have long highlighted the importance of environmental factors in mediating the paradox of why some such individuals delay independent breeding to help raise the offspring of others. In contrast, studies involving comparisons among species have not shown a similarly clear evolutionary-scale relationship between the interspecific incidence of cooperative breeding and any environmental factors. Here, we use a phylogenetically controlled comparative analysis of a complete, socially diverse group of birds-45 species of African starlings-to show that cooperative breeding is positively associated with living in semiarid savanna habitats and with temporal variability in rainfall. Savanna habitats are not only highly seasonal, but also temporally variable and unpredictable, and this temporal variability directly influences individual reproductive decisions in starlings and helps explain interspecific patterns of sociality. Cooperative breeding is likely to be adaptive in temporally variable environments because it allows for both reproduction in harsh years and sustained breeding during benign years. This "temporal variability" hypothesis might help explain the phylogenetic and geographic concentrations of cooperatively breeding vertebrates in savanna-like habitats and other temporally variable environments worldwide.

Meerkats

Meerkats

The age and evolution of sociality in Stegodyphus spiders: a molecular phylogenetic perspective

Social, cooperative breeding behaviour is rare in spiders and generally characterized by inbreeding, skewed sex ratios and high rates of colony turnover, processes that when combined may reduce genetic variation and lower individual fitness quickly. On these grounds, social spider species have been suggested to be unstable in evolutionary time, and hence sociality a rare phenomenon in spiders. Based on a partial molecular phylogeny of the genus Stegodyphus, we address the hypothesis that social spiders in this genus are evolutionary transient. We estimate the age of the three social species, test whether they represent an ancestral or derived state and assess diversification relative to subsocial congeners. Intraspecific sequence divergence was high in all of the social species, lending no support for the idea that they are young, transient species. The age of the social lineages, constant lineage branching and the likelihood that social species are independently derived suggest that either the social species are 'caught in sociality' or they have evolved into cryptic species.

NEST INTERFERENCE BY FLEDGLING LOGGERHEAD SHRIKES

Using video cameras, we documented at least two fledgling Loggerhead Shrikes (Lanius ludovicianus) visiting their parent's second active nest. We recorded 70 visits during a 10-day period, with visits averaging 7 min. We observed the fledglings sitting on the nest contents on 21 occasions. We concluded that these visits were not indicative of cooperative breeding behavior, because the fledglings were destructive to the nest structure and contents, and the adult female exhibited aggressive behavior toward the fledglings. An early reduction in post-fledging parental care by their father (who was of captive-bred origin) and slow development of the fledglings' hunting skills might have caused them to seek food resources from their mother. However, this is the first time that we have observed these behaviors in this intensively managed population.

Out of Gondwanaland; the evolutionary history of cooperative breeding and social behaviour among crows, magpies, jays and allies

Cooperative breeding is comparatively rare among birds in the mainly temperate and boreal Northern Hemisphere. Here we test if the distribution of breeding systems reflects a response to latitude by means of a phylogenetic analysis using correlates with geographical range among the corvids (crows, jays, magpies and allied groups). The corvids trace their ancestry to the predominantly cooperative 'Corvida' branch of oscine passerines from the Australo-Papuan region on the ancient Gondwanaland supercontinent, but we could not confirm the ancestral state of the breeding system within the family, while family cohesion may be ancestral. Initial diversification among pair-breeding taxa that are basal in the corvid phylogeny, represented by genera such as Pyrrhocorax and Dendrocitta, indicates that the corvid family in its current form could have evolved from pair-breeding ancestors only after they had escaped the Australo-Papuan shield. Within the family, cooperative breeding (alloparental care/family cohesion) is strongly correlated to latitude and its predominance in species maintaining a southerly distribution indicates a secondary evolution of cooperative breeding in the lineage leading away from the basal corvids. Multiple transitions show plasticity in the breeding system, indicating a response to latitude rather than evolutionary inertia. The evolutionary background to the loss of cooperative breeding among species with a northerly distribution is complex and differs between species, indicating a response to a variety of selection forces. Family cohesion where the offspring provide alloparental care is a main route to cooperatively breeding groups among corvids. Some corvid species lost only alloparental care, while maintaining coherent family groups. Other species lost family cohesion and, as a corollary, they also lost the behaviour where retained offspring provide alloparental care.

Observations on the breeding biology of the Seychelles Fody on Cousine Island

The Seychelles Fody, Foudia sechellarum, is a ploceid weaver occurring naturally on three islands in the Seychelles group in the Indian Ocean. The population on Cousine Island was studied between 30 June and 25 August 1997. The size of the population on the island was estimated at 458–614 individuals and densities varied in different habitat types. As Seychelles Fodies in non-breeding plumage are difficult to sex, we provide sexing criteria based on wing length. Breeding pairs form small, probably temporary, territories that are defended by both partners against other fodies, including the introduced Madagascar Fody, Foudia madagascariensis. The Seychelles Fody often breeds semi-colonially and we observed up to five nests close together. The birds are socially monogamous and both sexes share in nest building, nest defense and provisioning of the young. Only females incubate. Many nests were deserted before eggs were laid, including some that had been accepted by the female. Additional males and females were sometimes seen helping provision the young, but this cooperative breeding behaviour appeared to be uncommon. Non-breeding individuals congregate in large flocks, sometimes joined by breeding birds.